Capacitor



Sept. 15, 1942.

C. L. SCHEER CAPACITOR Filed June 30, 1939 Gttomeg Patented Sept. 15,1942 &295.759

CAPACITOB Charles L. seheer, naddonfleld. N. J., aig or to IloCorporation of America, a oorpor tion oi wre Application Ine 30, 1939,Serial No. 282.299

Claims. (Cl. 175-41) i This invention relates to capacitors oi the typewherein the armatures comprise metal applied in a fineiy divided stateto the mica or other dielectric. and to methods oi' making suchcapacitors.

The principal object ot the invention is to provide an improvedcapacitor, of the general type' described. which exhibits a lower power!actor than has heretotore been thought possible oi practicaiachievement.

Another and important object of the present invention is to provide asimple, inexpensive and trouble-free method of accomplishing theaforesaid object, and one which iends itself readily to the massproduction oi! capacitors of the general type described.

Other objects and advantages will be apparent and the invention will bebest understood by reference to the following speciflcation and to theaccompanying drawing. wherein r'igure 1 is a sectional view ot part oi acapacitor and illustrates the lack oi homogeneity in the metallic iilmsoi the prior art;

Figure 2 is a view of the capacitor ot Fig. 1 subsequent to beingtreated in accordance with the principle oi the invention andillustrates the homogeneity and physical continuity of the metallicfilms;

Figure 3 shows, in sectional elevation, one iorn of an apparatus fordepositing metal in a flnely divided state upon mica or other dielectricelements;

Figure 4 shows, in front elevation, a rack for supporting a number ofdielectric elements in the apparatus of Fig. 1;

Flgure 5 is a cross-sectional view taken on the line 5-5 of Fig. 4; and

Figure 6 is a side elevational view of an elemental capacitorconstructed in acoordance with the principle of the invention.

The present invention is predicated upon the fact, revealed bymicroscopic examination, that the metallic "mms" or "layers"` or"surface coatings of the prior art lack perfect physical continuity andhomogeneity. This may be attributed to the fact that such films areusually applied to the mica or other base in the form ot spray, vapor orsolution constituted oi discrete globules, or

spaced apart molecules of metal which, as inditreated illms, may be saidto lose their identity and form a sheet characterized by thesubstantially `perfect physical and electrical continuity of themolecules of which it is constituted. This desired result is achieved inaccordance with the method of the invention by subjecting a dielectricelement. upon which the opposite metallic armature layers have beendeposited, to a relatively high temperature for a period sufliclentlylong to produce softening and virtual flow of the metal, so that awelding, i'using, commingling or recrystallization of the formerlyseparate, or partly separated. molecules or globules of the metal is eected. as indicated by the smooth suriaces B in 2. This improvedsmoothness is usually evidenced in the finished film by its surfacesheen.

While the method ot the invention will be described as applied to ametallic iilm which has been deposited on the mica by thermalevaporation. distiilation or sublimation, it will be apparent to thoseskilled in the art that the invention is likewise applicable to metallicfilms which have been deposited by means of the Schoop spray process, orby electroplating methods, or by cathodic disintegration, or bysubstantially any other'hown method or process for creating andapplying' metal in a flnely divided state.

In carrying the invention into eiiect, the mica 2 is first split to therequired thickness and cut to size. The individual mica plates are thenpreferably provided each with a punched orifice 4 adjacent one endthereof, whereby they may be Suspended on pins E, which projectrearwardly from a !rame I which is provided with apertures o individualto the discrete mica plates. As shown more clearly in Figs. 4 and 5, thedimensions or apertures o are somewhat less than those of the micaelements so that the side edges and top edge |4 oi' each element areeflfectively sliielded by the marginai edges IS of the frame whichsurrounds each mica element. When all of the mica elements are in placein the frame 8, amasking plate s, which' is provided with a number ofapertures zu, is clamped tightly over the !rame as by bolts 22. Theapertures 20 in the masking plate s are preferably of the same size, butare oil'set in the vertical direction from the apertures Ifl in theframe 8 whereby the marginal side and bottom edges z', l4',respectively, of the mica surface opposite the surface containing themasked edges i2 and !4, are exposed.

With the mica plates mounted on rame 8 and masked by the masking plate!8 in the manner above described, the assembly is supported on asuitable bracket 24 (Fig. 3) fixed to the base 26 oi' an evacuableenclosure 28. As illustrated in Fig. 3, the enclosure 28 comprises aninverted vessel 30 adapted to be clamped to the base 26 as by bolts u.suitable gaskets 34 are provided to ensure a gas-tight seal between thebase !I and the vessel u. An outlet !I communicates with the interier ofthe enclosure and is connected with a suitable pump, not shown, forevaculatinz the vessel. A valve u is provided for restoring atmosphericpressure when the mica has been processed. Supported in spaced relationabove the base 2', as on rods 40 which extend between and along theframes C-il which support the mica, are a plurality of tungsten or otherrefractory metal fllaments u which are each bent in a convenient formsuitable for holding a piece u of the metal to be evaporated anddeposited upon the exposed areas of the opposite surfaces of the mica.

The number and spacing of the illaments 42 containing the metal to beevaporated is preferably such that all of the mica plates are thoroughlyand substantially equally bathed in metal vapor. The fllaments 42 arepreferably connected to a common source of heating current, not shown,so that when the enclosure 20 has become evacuated, evaporation of allof the metal elements 44 occurs, thereby effecting the coatin of bothsides of each mica plate simultaneously.

The absolute pressure maintained in the enclosure 28 during evaporationof the metal should, for optimum results, preferably be no higher andpreferably less than 0.0001 mm. of mercury (one-tenth of a micron).However, the use of vacuum pressure considerably higher than one-tenthof a micron may be employedas it has been discovered that by varying thedegree of vacuum up to, say, two microns. the ultimate capacitance ofthe elements may be varied over a substantial range. The general rule isthe higher the vacuum, the higher the ultimate capacitance. Thisphenomenon obtains by reason of the relative quantity of gas and otherforeign substances which are occluded in the metal during itsevaporation and deposited upon the mica. substantial freedom fromoccluded gases and foreign solids is achieved at the lowest pressurementioned.

The deposition of the metal having been completed the vacuum is brokenby opening the valve u, the frames 8 are taken from the brackets 24, themasks !8 are lifted and the now coated mica plates 2 are removed.subsequently and in accordance with the invention, these metallizeddielectric plates are subiected to a temperature sufflclent to cause awelding, fusing, commingling or recrystallization of the moleculesorglobules of which the metal films are constituted. Excellent resultshave been achieved simply by placing a batch of several hundred of theseplates 2 in a tray in an ordinary oven (not shown) and subjecting themto temperatures of the order of 275-325 C. for a period of from, say,flfteen to thirty minutes. The temperature and duration of this heattreatment are not especially critical but may vary somewhat asdetermined by the nature of the metal and thickness of the appliedfilms. Twenty minutes at apprcximately 300 C. is usually suflicientwhere the film is silver and of a thiclmess of the order of a fewonemillionths of an inch. The heating may be done in vacuo, if desired,or partly in vacuo and partly at atmospheric pressure; however, as aboveindicated, excellent results have been achieved on a commercial scale inan ordinary oven Operating at substantially atmospheric pressure.

Flg. 6 shows a capacitor comprising a stacir of ascunsa two elementalcapacitors, each of which comprises a. sheet of mica 2 and a pair ofdiscrete metal films B which have been treated in accordance with thepresent invention to eflect a commingling of the formerly separate, orpartly separatedmolecules or globules of metal.

Comparative tests of evaporated-metal films before and after thedescribed heat treatment showed a reduction of the order ofsubstantially flfty percent in direct current resistance. Tests ofcomplete capacitors showed a reduction in power factor of the order ofseventy-flve percent. By way of example, a number of untreated (butotherwise similar capacitors) exhibited a power factor of the order of.0006-.0008 at 1000 kilocycles. whereas those treated in accordance withthe present invention exhibited a power factor of .0001 to .0003.

The foregoing description of the presently pre-- ferred apparatus andmeans for achieving the obiects of the invention should be interpretedas illustrative and not in a limiting sense except as required by theprior art and by the spirit of the appended claims.

What is claimed is:

1. Method of decreasing the dielectric iosses oi a capacitor comprisedof a pair of conductive film-like armatures constituted of metal in afinely divided state and adhering to the opposite surfaces of aninterposed dielectrlc layer, said method comprising subiecting saidcapacitor to a temperature sufnciently high and for a periodsufflciently long to cause softening and virtual flow of the metal.

2. Method of decreasing the dielectric iosses oi a capacitor comprisedof a pair of conductive film-like armatures constituted of metal in afinely divided state and adhering to the opposite surfaces of aninterposed dielectric layer, said method comprising subjecting saidcapacitor to a temperature of the order of from substantially 275 C. tosubstantially 325 C. for a period sufllciently long to cause softeningand virtual flow of the metal.

3. Method of decreasing the dielectric losses of a capacitor comprisedof a pair of conductive film-like armatures constituted of metal in ailnely divided state and adhering to the opposite surfaces of aninterposed dielectric layer, said method comprising subjecting saidcapacitor to a temperature of the order of from substantially 275" C. tosubstantialiy 325 C. for a period of the order of from substantiallyflfteen to thirty minutes.

4. Method of manufacturing a capacitor which comprises depositing a filmconstituted of metal in a nely divided state upon the opposite surfacesof a dielectric element, and subsequently subjecting said deposited filmto a temperature sufllciently high and for a period sufllciently long tocause softening and virtual flow of said metal.

5. Method of manufacturing a capacitor which comprises mounting adielectric element and a piece of metal in a vacuum, then subjectingsaid metal to a temperature sumcient to cause thermal evaporation of themetal whereby to cause it to be deposited in the form of a film upon theopposite surfaces of said dielectric element, and subsequentlysubiecting said coated element to a temperature sumciently high and for.a period sumciently long to cause virtual flow of the metal constitutingsaid film.

CHARLES L. SCHEER.

